On the contrary, Coraline wasn't scowling because Coraline wasn't angry. Her expression was fairly neutral as she gauged the situation, for Coraline hadn't expected the House of Salazar to have fallen so far in the ten years of her absence.
When Coraline had been in school, Slytherin house had abounded in people who could be loosely described as an intimidating bunch. When outside their common room, they'd stuck together like glue and Slytherin had wiped the floor with the other houses. Inside the common room, the older students had spent their time "correcting" the younger ones. Telling them all their inherited ideas of superiority were worthless if they couldn't hold a wand the right way, then coaching them in the arts of deceit and guile.
Obviously, things had changed, and not for the better. Dancing could wait. She would have to take them right back to the beginning.